Is the fiancée considered in the ismah (bond of marriage) of the first suitor after he utters a divorce, knowing that she has not received the mahr (dowry) and has not paid any compensation?

As long as her father informed her that what transpired regarding offer and acceptance was an engagement (khitbah) and not a marriage contract, then there is no need for a divorce or khul‘, and she has no relation to the man. It is permissible for her to marry someone else. If the custom is such that an engagement and its acceptance are merely a preliminary step for the legitimate contract and are not binding, then the marriage is not concluded thereby.